1. Field of the Invention
The present invention is in the field of hydraulic accumulator devices and is directed more particularly to a hydraulic accumulator of the type which includes a pressure vessel having a gas charging port at one end and an oil port at the other, the vessel being divided into two chambers of varying sizes by a distensible elastomeric bladder.
2. The Prior Art
The use of hydraulic accumulators including rigid pressure vessels incorporating, as noted, a distensible bladder member to divide the interior into two chambers, is a well known expedient for purposes of energy storage and pulse dampening. Devices of the type described frequently incorporate, in addition, a rigid valve or button member mounted on the bladder and juxtaposed to the oil port, such rigid member functioning to seat against the oil port when pressures in the gas chamber exceed those in the hydraulic fluid communicated to the oil port. By thus providing a valve member, the possibility of extruding the bladder through the oil port is minimized.
Heretofore devices, whether or not utilizing the button type anti-extrusion assembly, have been short lived. Compromise of the bladder components of such devices have often resulted where the bladder expands rapidly, resulting in portions of the bladder other than the button or like expedients being engaged against and passing through the oil port.
Various means have been effectively employed to increase the life of the bladder components in the devices of the type described. Such expedients include the provision of poppet valves seated within the oil port, physical connection of the bladder to a guiding mechanism which assures that only selected portions of the bladder will be engaged against the oil port, and the like. It will, however, be readily recognized that the provision of poppets, guide mechanisms and the like greatly increases the complexity and, hence, the cost of accumulators.
In an effort to maintain the cost of accumulators at a desired low level, attempts have been made carefully to control the wall thickness of all portions of the bladder assembly with the expectation that by so doing a uniform and predictable expansion of the bladder may be achieved notwithstanding rapid pressure fluctuations. It was hoped that by achieving a uniform expansion of the bladder, movements of the button would be predictable, with concomitant effective seating of the button against the oil port whereby bladder damage could be avoided.
Such attempted mode of solution of the problem has been unsuccessful since precise controlling of the bladder thickness itself adds a substantial degree of cost to the manufacture of the bladder. Further, it has been found that after many operative cycles the stretch characteristics of the bladder change, recreating the problem of uneven expansion, misdirection of the button and consequent destruction of the bladder.